It is common practice in the construction industry to construct waterproof exterior decks. Such decks are typically constructed between vertical supports such as walls and posts. A subfloor is generally constructed on joists running between the vertical supports such that the subfloor slopes away from the building structure and toward the free edge. A waterproof deck flashing system is typically used to protect the vertical support to free edge transition as wells as define the outer edge of the topping surface. The sheet metal flashing and subfloor are protected by a waterproof sheet which allows water to drain off the deck without penetrating the subfloor. A drainage sheet otherwise called a protective sheet may be installed on top of the waterproof sheet to protect it from damage. A topping surface, typically a lightweight concrete or mortar/tile surface, is installed on top of the protective sheet. The topping surface is poured onto the protective sheet. The outside edge of the sheet metal flashing system defines the outside edge of the topping surface. These decks are designed so that water penetrating the topping surface and seeping down to the waterproof sheet will flow toward and off the free edge of the deck without penetrating and damaging the subfloor and vertical support structure. A number of sheet metal flashing designs have been used to accomplish this goal.
Typical waterproof decks utilize a sheet metal flashing system made of galvanized sheet metal (GSM). There are several components which make up the system. The flashing which protects the subfloor to vertical support transition is usually referred to as “deck-to-wall” or “wall flashing” even though it might otherwise be applied to a subfloor to post transition. It is typically “L” shaped 18 gauge GSM sheet metal which is placed such that the vertical leg extends upward along the wall (or post) and the horizontal leg extends horizontally over the top of the subfloor. Wall flashing which extends around a corner or post may also be called “saddle flashing.”
The flashing which protects the free edge of the deck subfloor is typically called “edge flashing”. It is typically “L” shaped 18 gauge GSM which is placed about the free edge of the subfloor such that the horizontal leg extends back several inches from the outside edge and over the top horizontal surface of the subfloor. The vertical leg of the edge flashing typically extends downward several inches from the free edge over the subfloor edge and sometimes covering the outside edge of the subfloor-to-joist transition below the subfloor. The bottom portion of the vertical leg of the edge flashing is often called the “drip edge” because it is the edge which escaping water drips off and away from the building. Typical drip edges are flanged away from the deck at an angle to prevent water from dripping onto the subfloor materials.
In a typical prior art deck construction, waterproof sheet material is placed over flashing to prevent water from penetrating the flashing system and subfloor. Once wall flashing and edge flashing components have been nailed in place, a waterproof sheet is rolled over the subfloor extending downward from the top edge of the vertical wall flashing, over the horizontal leg of the wall flashing, over the deck subfloor surface, over the horizontal leg of the edge flashing, and downwards over the vertical extending leg of the edge flashing.
Before a liquid topping surface can be installed on top of the deck, the outside edge of the deck must be established to prevent the liquid topping (usually concrete or mortar) from spilling over the free edge of the deck and to define the outside edge of the deck topping surface. Typically, this outside edge is accomplished through use of a T-bar flashing strip installed at the free edge of the deck. A T-bar flashing strip is an elongated strip of sheet metal which is T-shaped in cross section. It is installed such that the stem of the T lies horizontally on the horizontal leg of the edge flashing with the crosshead of the T extending out and beyond the free edge. The stem of the T is usually secured by nailing fasteners through the stem, through the protective and waterproof sheets, through the horizontally extending portion of the edge flashing and into the subfloor. The placement creates a gap between the vertical leg of the edge flashing and the downwardly extending portion of the T-bar crosshead. The system is designed so that water seeping between the horizontally placed T-bar stem and the waterproof sheet will escape over the free edge. If the T-bar strip was placed such that the crosshead abutted the free edge, the flow of water would be blocked at the free edge.
In typical installations using T-bar flashing strips, the outside edge of the topping surface is defined by the upwardly extending portion of the T-bar crosshead. The upwardly extending lip portion of the crosshead allows for installation of liquid topping surface directly onto the waterproof sheet and holds the topping material in place while it sets. In cases where a protective sheet is used over the waterproof sheet, the protective sheet serves to protect the waterproof sheet from damage by the topping material or from damage inflicted by installers who might walk on the deck prior to installation of the topping surface.
Numerous problems have been identified with this typical prior art deck construction. One major problem is that water will often move through the water permeable topping material, penetrate the waterproof sheet, and seep into the subfloor and structural supports creating staining and further water damage. While much or most of the water hitting the deck topping material will run along the top surface down slope and toward the free edge of the deck, some water hitting the deck topping surface will penetrate the water permeable topping material and seep down to the waterproof sheet. Water accumulating on the waterproof sheet tends to move down slope toward and over the free edge of the deck. But often times the water will also move downward through penetrations in the waterproof sheet (created by damage, wear or poor installation) and into the subfloor and vertical supports structure.
The problem of water penetrating the waterproof sheet at or near the free edge of the deck is exacerbated when it is blocked by a T-bar stem mounted directly on top of the waterproof sheet. Water accumulates at this location and either moves laterally toward a deck corner or will seep through fastener penetrations or other penetrations in the waterproof sheet.
Various prior art flashing systems have been utilized in an attempt to alleviate water seepage. For example, wall flashing has been designed to extend above and below the free edge of the deck and utilized open channels placed at the abutment of the T-bar strip to wall flashing to facilitate better drainage at the wall to free edge juncture (see U.S. Pat. No. 6,725,617). Other designs utilize weep holes punched in the upwardly extending portion of the T-bar crosshead to allow water to weep out at the crosshead. Systems which rely on channels or weep holes are often ineffective because either the holes are not large or numerous enough and/or they get blocked by topping materials. In situations relying on installation of weep holes in the field it is common for such holes to be positioned ineffectively positioned (such that, for example, the weep holes are too high above the horizontally positioned stem to allow for adequate water drainage).
Some prior art systems have utilized spacers placed between the horizontally extending T-bar stem and the waterproof sheet to provide additional drainage passage between the T-bar stem and the waterproof sheet (See U.S. Pat. No. 5,546,719). But systems relying on spacers tend to be ineffective because the spacers are either not high enough, cause excess weigh to be distributed onto portions of the waterproof sheet thus tearing or damaging it, and/or allowing the T-bar stem to bend downward between spacers and inhibit water passage.
The use of fasteners (such as nails or screws) to fasten the T-bar stem to the edge flashing is, again, a major cause of water seepage because fastener penetrations provide a direct conduit for water to seep through the waterproof sheet to the subfloor. Some prior are systems utilize special materials, such as self sealing waterproof sheeting material, to mitigate water seepage through fastener holes. Waterproof sheeting materials such as Bituthane polyurethane manufactured by R.W. Grace can, for a limited period of time, adhere to the sides of fasteners penetrating the waterproof sheet. But such self sealing products often don't seal completely and will eventually fail over time. Further failure of the seal between materials and the fasteners results from movement of the flashing system over time as a result of transfer forces on the deck surface (for example, deflection caused by persons or heavy objects on the deck) or differential movement and settling of the deck structure post construction all of which is commonly experienced by deck structures over time. Such movement is further exasperated by inadequately spaced or driven fasteners. Nailing can be inconsistently spaced, over driven or under driven. In adequate nailing is common in the construction industry where construction expertise, time and care can be limited. Movement of the flashing on top of the waterproof sheet will rip or tear the waterproof sheet particularly in those areas already experiencing degradation as a result of water seepage.
Improper nailing is not the only installation problem. The various deck flashing components need to be properly fitted to the deck edge and to the vertical supports so that they are in line with one another and so that fasteners can be properly spaced. Adjacently placed materials, such as lengths of edge flashing, must be caulked or sealed. Any gaps left between edge flashing will provide an avenue for water to penetrate into the subfloor and/or a rough surface transition which will eventually cause damage to the waterproof sheet. No amount of caulking or sealant will completely make up for installation problems which provide additional avenues for water to seep into and damage subfloor and support materials.
Further, flashing systems can be difficult to install because decks come in a variety of sizes with significant detail changes that require the installers to coordinate their efforts with other trades and to be extra careful in fitting the various components to the deck subfloor and adjacent materials. Multiple tradesmen (including framers who build the support structure, waterproofers who install the waterproof sheeting and sealants, sheet metal subcontractors who typically install the sheet metal, and pavers who typically install the topping surfaces) can be involved in the installation process. And deck systems can be susceptible to damage from worker traffic particularly prior to installation of topping materials. The waterproof sheeting can be susceptible to tears. Flashing components may expand or contract in the open elements. Installation of building components in adjacent locations to the deck can cause movement in the subfloor which can create gaps in adjacently installed materials. Also, installation of flashing components installed directly adjacent to one another (and which do not overlap) are susceptible allowing gaps that are often left unfilled. Thus, deck flashing systems that have too many components or which require too much cutting and fitting can be particularly problematic to install and maintain.